timing curve(s) for 18RTE

**chris_rg** · 30-03-2006, 04:57 PM

Originally Posted by wilbo666

Most turbo cars have a RRFRP. When you are on 15psi boost the fuel rail pressure only appears to be 40psi - 15psi = 25psi! So if you up the Fuel rail pressure 1:1 with the boost (what most stock turbo cars do) then the fuel pressure remains constant relative to the manifold pressure.

It removes a non-linearity from the system

Cheers
Wilbo

A normal fuel pressure regulator will keep the fuel rail pressure a constant level above manifold pressure, ie 40psi. Thats why one side of the regulator is connected to the manifold.

for example, when i'm flat out in a N/A car you have just under atmospheric pressure in the manifold, so rail pressure will be about 40psi greater than atmosphere. However when i'm cruising down a hill and have heaps of vacuum, the fuel rail pressure decreases relative to atmosphere. However, it is still 40psi relative to the manifold.

Now 'if' i had a turbo with my standard regulator when the boost came in the regulator would be referenced to this and lift the fuel pressure as needed.

This is the 1:1 relationship you are talking about.

I was under the impression that RRFPR's go above 1:1 up to 1.2:1 etc. And were usually used when you were pushing the limits of your injectors to put more pressure across the injector. for example 15psi of boost and the regulator compensates with 20psi of extra fuel pressure so you end up with more than 40psi across the injector. This of course put heaps of load on your fuel pump. And the non-linearities i was talking about.

i'm sure i've seen threads which back this up.

i'll go searchin'

**chris_rg** · 30-03-2006, 05:00 PM

check out...

http://forums.toymods.org.au/index.p...t=0#msg_823197

or to save time quote from the 'all-knowing' oldcorollas... makes sense to me...

normal pressure reference fuel pressure regulators will increase fuel pressure as a 1:1 ratio of the reference pressure.

rising rate fuel pressure regulators are called that because the rate at which the fuel pressure increases is greater than the boost reference pressure, ie 1.5:1, 2:1 etc.

a RRFPR increases fuel faster, and you run into fuel pump problems sooner. since injectors are designed for a certain range of pressure, you should keep the pressure differential across them close to their design.

a higher differential, as with RRFPR, gives higher flow for same PW.. to a point.. and the only time they are warranted is when you are trying to richen the fuel curve of a stock setup using stock ECU which has MAP sensor, after you decrease intake flow path resistance....

or so i think Wink.... in all other situations, you are better off using a 1:1 FPR so that you always have the same pressure differential across the injector, and then you have a better idea of what a given increase in PW will do to fuel flow..

maybe Wink

and

oh, and as far as i know, most stock FPR's as 1:1 ratio. there is no need for a rising rate regualtor when you have the option of changing the tuning by programmable means.

**chris davey** · 30-03-2006, 05:21 PM

Some people get aftermarket 1:1 FPR's so that they can adjust the base pressure though. But yes you are right.

**wilbo666** · 30-03-2006, 05:30 PM

Yah I get what you are saying now

thechuckster has a variable RRFPR as far as I am aware.

I've also suggested to thechuckster that having the FPR set to other than 1:1 (unless he is struggling for injector size up top) will only complicate things...

Cheers
Wilbo

**thechuckster** · 30-03-2006, 06:12 PM

am reasonably sure that the 'rate' is fixed - all i can adjust is the base pressure. It is a Malpassi.

agreed - it will be interesting (and scary) to see whether i get leakage around the injectors but with fuel rail #2 being drilled correctly, i hope i'ts all OK.

Pump is an external bosch VL pump. It sounded happy enough during static testing - rail gets up to pressure in about a second of power-on and the MS unit provides a 2-second priming pulse on booting up.

fwiw- the rail safely holds a sustained 40psi pressure ... and i'll have 2 fire extingishers in the car with me.